This invention relates to a process for the generation of mechanical energy in the ammonia oxidation step of a process for the production of nitric acid, i.e. the step wherein ammonia is burned to form NO.sub.x.
When oxidizing ammonia to form NO.sub.x gases required for nitric acid production, the oxidation normally takes place at a temperature of 800.degree. to 970.degree. C. However, low temperatures are preferred for the absorption of NO.sub.x gases in water to form HNO.sub.3 in order to meet the reaction requirements. Therefore, the NO.sub.x gas stream must be cooled prior to entering the absorption unit.
As a rule, this cooling process takes place at a high temperature, using the proces heat to generate steam and/or to heat the tail gas from the absorption step and the resultant gas is subsequently expanded, for instance, in a turbine. In this case, the NO.sub.x gases at about &lt;200.degree. C. are cooled without exploiting the process heat; the heat transferred is dissipated via a cooling system. Consequently, the heat still contained in the NO.sub.x gases is not converted to energy and, depending on the process involved, larger quantities of cooling water are required causing higher operating costs, or larger heat exchangers must be installed which results in higher investment costs.